Optoelectronic modules have been developed for transmitting optical information or receiving optical information or both. An optoelectronic module typically includes at least one active device, such as an optical receiver or an optical transmitter, and a lens for coupling light between the active device and an optical fiber of a fiber optic cable. An optoelectronic module typically includes a connector with a bore that is configured to receive a ferrule, which holds an optical fiber of the fiber optic cable. The bore positions an end of the optical fiber at the focal point of the lens of the optoelectronic module.
During fabrication of an optoelectronic module, the optical components are aligned with one another and with an optical fiber of a fiber optic cable to optimize the coupling efficiency between the active device and the optical fiber. In one active alignment approach, the connector holding the ferrule is mechanically manipulated until an optimal coupling between the optical fiber held by the ferrule and the active device within the optoelectronic module is achieved. After the optimal coupling has been achieved, the connector is bonded to the optoelectronic module. This process requires either human interaction or expensive equipment that automatically dithers the connector into the optimal position.
Some types of optoelectronic modules use machined parts to align the active devices and the coupling optics. The alignment accuracies of such machined parts are low. In order to compensate for the large accumulated alignment mismatches inherent in such designs, the connector typically is actively aligned to the focusing lens in three dimensions to achieve a high coupling efficiency with the optical fiber. Active alignment in three dimensions, however, increases the cost and complexity of the optical alignment process.
Planar wafer-level optical assemblies have been developed for coupling light between an external fiber optic cable and the active components of optoelectronic modules. These optical assemblies simplify the tasks of packaging the active devices and aligning the coupling optics to the external fiber optic cable. The coupling optics in the transmitter optical paths of these designs include a single lens for focusing a diverging light beam from a laser onto the receiving end of an optical fiber. The use of such a focusing lens imposes significant constraints on the design of the optical components along the transmitter optical path between the laser and the focusing lens. In addition, in designs that use a single ball lens to focus light from a laser onto an external optical fiber, the ball lens introduces significant aberrations that reduce the coupling efficiency between the laser and the external optical fiber.